Technical Field
The present invention relates to a method for searching a touch point of a DCT clutch.
Description of the Related Art
In the transmission system where a power from an engine is transferred through a clutch, a control is generally made based on a TS (torque-stroke) characteristic graph (hereinafter, referred as “TS curve”) showing a change in a clutch torque for a clutch position (stroke). Thus, in order to perform highly reliable control, the TS curve should be learned which is changed in accordance with a control environment (clutch temperature, etc.).
In the TS curve, a touch point functions as a control element and has an important meaning as the starting point of the TS curve that transfers the power of the engine to the clutch by making a clutch plate and an engine plate come in contact with each other.
A DCT (dual clutch transmission) is designed to learn the TS curve through the periodic study about the touch point of the clutch shaft which is not driven between two clutches.
In other words, since the DCT is provided with a clutch which is capable of disconnecting a power automatically by an actuator and, in the case of using a dry type clutch, the touch point as an operation starting point of the clutch is changed due to, e.g., temperature change or abrasion of the clutch, the proper study for the touch point is necessary in order to ensure the stable operability of the clutch.
Conventional touch point search was typically done based on the velocity change value of a neutral shaft made at the time when the clutch is applied after confirming the gear neutral condition of a non-drive shaft.
However, the dual clutch transmission (DCT) has an advantage that a next transmission is prepared by engaging a gear in advance with the clutch which is not currently driven. However, in a state where a gear is engaged with a clutch in advance, it is impossible to search for a touch point in a conventional way and a control quality cannot be guaranteed at the next transmission when the state is continued.